Method of applying a firmly-adhering metal coat to insulating plates, particularly for use in electric condensers



Patented Jan. 21, 193% UNITEU STATEfi time PATENT @FFICE EMIL PFIFFNER, 01H FRIBOURG, SWITZERLAND, ASSIGNOR, BY MESN'E ASSIGNMENTS, TO RADIO PATENTS CORTORATION, NEW YORK, N. Y., A CORPORATION OF NEW YORK METHOD OF APPLYING- A FIRMLY-ADHERING METAL COAT T0 INSULATING PLATES,

PARTICULARLY FOR USE IN ELECTRIC CONDENSERS .No Drawing. Application filed November 11, 1926, Serial No. 147,846, and in Germany November 12, 1925.

However this great dielectric firmness or strength can be taken advantage of to the full extent only in case an intimate contact is established between the insulating material and I the metal coat, so that gaps, filled with air or gas, cannot be formed between the said material and coat, and discharges cannot take place within the said gaps.

It is already known to superficially saponify a film of this material before the chemical precipitation of the metal by means of acids or alkalis. From this, the method according to the present invention differs in that, by employing metallic salt solutions containing anexcessive amount of an acid and alkali, the superficial saponification of the ether or ester is carried out by the reducing action of the freed cellulose which causes a colloidal separation of metal and metaloxide respectively. Thereby a connection takes place between the cellulose and the metal or metallic oXid, and according to the density of the precipitation the coloration ranges from light yellow over brown to black.

The firmly adhering intermediate layer constitutes the/support for the application of the metalcoat which by the addition of a reducing agent is applied in a chemical or electrolytio manner, according to known methods. A superficial saponificati'on, of the celis detrimentally affected when using alkalis' or acids alone. Therefore according to the present invention the saponification is carried out in the presence of metallic salts,

oxide the cellulose is protected against se" vere attacks by the alkalis or acids.

The metallic salt solutions which superficially saponify the cellulose, can be any solution containing an excess of alkali, as for instance potassium-, sodium-, or ammonium hydroxide; or on the other hand a solution containing an excess of acid, such as for instance sulphuric acid, would be suitable.

In the preferred form of the invention the metallic salt solution used is an ammoniacal solution of silver nitrate.

According to the present invention the same metallic salt solution can be employed for producing the intermediate layer and the conducting metal-coat.

I claim:

1, In the process of applying a metallic coating to a sheet of a cellulose ester wherein the sheet is superficially saponified to liberate free cellulose by the action of an acid or an alkalisaponifying solution, the method of forming a firmly adhering initial coating on said sheet which comprises treating the sheet with a saponifying solution containing a metallic salt reactive with free cellulose to precipitate a metallic reduction product whereby the cellulose ester sheet is superficially saponified and an initial metallic production product is simultaneously precipitated on said sheet.

2. In the process of applying a metallic coating to a sheet of a cellulose ester, the

method of forming a firmly adhering initial coating on said sheet which comprises treating the sheet with an 'ammoniacal solution of silver nitrate.

In testimony whereof I afilx my signature.

EMIL PFIFFNER.

whereby the insulating material is effected in soft manner inthat owing to the simultaneous separation of the metal or metallic 

